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法学如果我截断一张表，还应该添加索引吗？
如果你截断了一张表，则不需要添加索引，因为表在被截断后会重新创建，索引也会自动添加。
我们首先创建一个表：-
mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> FirstName varchar(20), -> LastName varchar(20) -> ); Query OK, 0 rows affected (0.65 sec)
以下查询用来创建索引：-
mysql> create index Index_firstName_LastName on DemoTable(FirstName,LastName); Query OK, 0 rows affected (1.04 sec) Records: 0 Duplicates: 0 Warnings: 0
使用插入命令在表中插入一些记录：-
mysql> insert into DemoTable(FirstName,LastName) values('John','Smith');
Query OK, 1 row affected (0.47 sec使用 select 语句显示表中的所有记录：-
mysql> select *from DemoTable;
输出
这将产生以下输出：-
+----+-----------+----------+ | Id | FirstName | LastName | +----+-----------+----------+ | 1 | John | Smith | +----+-----------+----------+ 1 row in set (0.00 sec)
在截断表之前，你需要检查表的 status：-
mysql> show create table DemoTable;
输出
这将产生以下输出：-
+--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table| +--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | DemoTable | CREATE TABLE `DemoTable` (`Id` int(11) NOT NULL AUTO_INCREMENT,`FirstName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,`LastName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,PRIMARY KEY (`Id`),KEY `Index_firstName_LastName` (`FirstName`,`LastName`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci | +--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
现在截断表：-
mysql> truncate table DemoTable; Query OK, 0 rows affected (2.01 sec)
现在再次检查表的状态。你不需要添加索引：-
mysql> show create table DemoTable;
输出
这将产生以下输出：-
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | DemoTable | CREATE TABLE `DemoTable` (`Id` int(11) NOT NULL AUTO_INCREMENT,`FirstName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL,`LastName` varchar(20) COLLATE utf8_unicode_ci DEFAULT NULL, PRIMARY KEY (`Id`),KEY `Index_firstName_LastName` (`FirstName`,`LastName`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci | +--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
更新于： 2020 年 6 月 30 日
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